Scaling theory of driven polymer translocation

We present a theoretical argument to derive a scaling law between the mean translocation time $\tau$ and the chain length $N$ for driven polymer translocation. This scaling law explicitly takes into account the pore-polymer interactions, which appear as a correction term to asymptotic scaling and are responsible for the dominant finite size effects in the process. By eliminating the correction-to-scaling term we introduce a rescaled translocation time and show, by employing both the Brownian Dynamics Tension Propagation theory [Ikonen {\it et al.}, Phys. Rev. E {\bf 85}, 051803 (2012)] and molecular dynamics simulations that the rescaled exponent reaches the asymptotic limit in a range of chain lengths that is easily accessible to simulations and experiments. The rescaling procedure can also be used to quantitatively estimate the magnitude of the pore-polymer interaction from simulations or experimental data. Finally, we also consider the case of driven translocation with hydrodynamic interactions (HIs). We show that by augmenting the BDTP theory with HIs one reaches a good agreement between the theory and previous simulation results found in the literature. Our results suggest that the scaling relation between $\tau$ and $N$ is retained even in this case.Comment: 5 pages, 4 figure

Driven translocation of a semi-flexible polymer through a nanopore

We study the driven translocation of a semi-flexible polymer through a nanopore by means of a modified version of the iso-flux tension propagation theory (IFTP), and extensive molecular dynamics (MD) simulations. We show that in contrast to fully flexible chains, for semi-flexible polymers with a finite persistence length $\tilde{\ell}_p$ the {\it trans} side friction must be explicitly taken into account to properly describe the translocation process. In addition, the scaling of the end-to-end distance $R_N$ as a function of the chain length $N$ must be known. To this end, we first derive a semi-analytic scaling form for $R_N$, which reproduces the limits of a rod, an ideal chain, and an excluded volume chain in the appropriate limits. We then quantitatively characterize the nature of the {\it trans} side friction based on MD simulations of semi-flexible chains. Augmented with these two factors, the modified IFTP theory shows that there are three main regimes for the scaling of the average translocation time $\tau \propto N^{\alpha}$. In the stiff chain (rod) limit $N/\tilde{\ell}_p \ll 1$, {$\alpha = 2$}, which continuously crosses over in the regime $1 < N/\tilde{\ell}_p < 4$ towards the ideal chain behavior with {$\alpha = 3/2$}, which is reached in the regime $N/\tilde{\ell}_p \sim 10^2$. Finally, in the limit $N/\tilde{\ell}_p \gg 10^6$ the translocation exponent approaches its symptotic value $1+\nu$, where $\nu$ is the Flory exponent. Our results are in good agreement with available simulations and experimental data

Aikuisväestön hyvinvointi, terveys ja palvelut – FinSote 2020 : Aikuisten palvelukokemuksissa ja hyvinvoinnissa alueellisia eroja

FinSote-tutkimus tuottaa laajasti tietoa väestön koetusta hyvinvoinnista, elinoloista, terveydentilasta, elintavoista, työ- ja toimintakyvystä sekä laajasti palvelukokemuksista kuten niiden saatavuudesta ja asiakastyytyväisyydestä. Tässä raportissa tarkastellaan kahta keskeistä teemaa: psyykkistä kuormittuneisuutta ja riittämätöntä terveyspalveluiden saantia

Polymer escape from a confining potential

The rate of escape of polymers from a two-dimensionally confining potential well has been evaluated using self-avoiding as well as ideal chain representations of varying length, up to 80 beads. Long timescale Langevin trajectories were calculated using the path integral hyperdynamics method to evaluate the escape rate. A minimum is found in the rate for self-avoiding polymers of intermediate length while the escape rate decreases monotonically with polymer length for ideal polymers. The increase in the rate for long, self-avoiding polymers is ascribed to crowding in the potential well which reduces the free energy escape barrier. An effective potential curve obtained using the centroid as an independent variable was evaluated by thermodynamic averaging and Kramers rate theory then applied to estimate the escape rate. While the qualitative features are well reproduced by this approach, it significantly overestimates the rate, especially for the longer polymers. The reason for this is illustrated by constructing a two-dimensional effective energy surface using the radius of gyration as well as the centroid as controlled variables. This shows that the description of a transition state dividing surface using only the centroid fails to confine the system to the region corresponding to the free energy barrier and this problem becomes more pronounced the longer the polymer is. A proper definition of a transition state for polymer escape needs to take into account the shape as well as the location of the polymer.Peer reviewe

Iso-Flux Tension Propagation Theory of Driven Polymer Translocation: The Role of Initial Configurations

We investigate the dynamics of pore-driven polymer translocation by theoretical analysis and molecular dynamics (MD) simulations. Using the tension propagation theory within the constant flux approximation we derive an explicit equation of motion for the tension front. From this we derive a scaling relation for the average translocation time τ, which captures the asymptotic result τ∝N1+ν0 , where N 0 is the chain length and ν is the Flory exponent. In addition, we derive the leading correction-to-scaling term to τ and show that all terms of order N2ν0 exactly cancel out, leaving only a finite-chain length correction term due to the effective pore friction, which is linearly proportional to N 0. We use the model to numerically include fluctuations in the initial configuration of the polymer chain in addition to thermal noise. We show that when the cis side fluctuations are properly accounted for, the model not only reproduces previously known results but also considerably improves the estimates of the monomer waiting time distribution and the time evolution of the translocation coordinate s(t), showing excellent agreement with MD simulations.Peer reviewe